Epidemiological observations and heterosis analysis of gastrointestinal nematode parasitism in Suffolk, Gulf Coast Native, and crossbred lambs

A crossbreeding program was conducted to evaluate the resistant status to g astrointestinal nematode parasite infection in crossbred (F-1) lambs and th eir Suffolk and Gulf Coast Native (Native) breed counterparts. A total of 2 53 lambs were included in the study over 2 years. Fecal egg count (FEC) and blood packed cell volume (PCV) of 18-20 monitor lambs of each breed group in each year were collected every other week from birth to 24-30 weeks of a ge. The FEC and PCV of all lambs were determined at weaning (11-12 weeks of age) and at three subsequent times when anthelmintic treatment was adminis tered. Nematode counts of wether lambs were obtained at 30 weeks of age in the first year. The epidemiological patterns of FEC and PCV of each breed g roup were similar in both years. The Suffolk group consistently showed the highest FEC and the lowest PCV, Conversely, the Native group had the lowest FEC and highest PCV, For the most part, all parameters for the Fl group fe ll intermediate to the Native and Suffolk groups. Nematode count followed t he same pattern. Heterosis analysis showed that FEC, PCV, nematode count an d weight gain of the Fl group favored the Native group. These results sugge sted that crossbreeding Suffolk to Native sheep may be a suitable way to pr oduce lambs with improved resistance to gastrointestinal nematode infection , but production may be compromised. (C) 2001 Elsevier Science B,V. All rig hts reserved.